1. Lecture 8: Volume Interactions
Friday, 28 January 2010
Lecture 8: Volume Interactions
Reading
Ch 1.8
Major spectral features of minerals (p. xiii-xv), from Infrared ( mm) Spectra of Minerals, J W Salisbury et al., 1991 – ( class website)
Optional reference reading: Roger Clark’s tutorial on spectroscopy (class website)

2. What was covered in the previous lecture
Wednesday’s lecture
1) reflection/refraction of light from surfaces
(surface interactions)
Today’s lecture:
2) volume interactions
- resonance
- electronic interactions
- vibrational interactions
3) spectroscopy
- continuum vs. resonance bands
- spectral “mining”
- continuum analysis
4) spectra of common Earth-surface materials
LECTURES
Jan Intro
Jan Images
Jan Photointerpretation
Jan Color theory
Jan Radiative transfer
Jan Atmospheric scattering
Jan Lambert’s Law previous
Jan Volume interactions today
Feb Spectroscopy
Feb Satellites & Review
Feb Midterm
Feb Image processing
Feb Spectral mixture analysis
Feb Classification
Feb Radar & Lidar
Feb Thermal infrared
Mar Mars spectroscopy (Matt Smith)
Mar Forest remote sensing (Van Kane)
Mar Thermal modeling (Iryna Danilina)
Mar Review
Mar Final Exam 2

3. Spectral radiance (W/m2/nm/sr)
Wavelength (nm)
Spectral radiance (W/m2/nm/sr)
Spectral radiance (W/m2/nm/sr)
Wavelength (nm)
Wavelength (nm)

4. Interaction of Energy and Matter
What causes absorption features in spectra?
Three effects of radiant energy on matter:
Rotational absorption (gases)
Electronic absorption
Vibrational absorption

5. Rotational Processes
Photons striking free molecules can cause them to rotate. The rotational states are quantized, and therefore there are discrete photon energies that absorbed to cause the molecules to spin.
Rotational interactions are low-energy interactions and the absorption features are at long infrared wavelengths.

6. Electronic Processes Four types:
Isolated atoms and ions have discrete energy states. Absorption of photons of a specific wavelength causes a change from one energy state to a higher one. Emission of a photon occurs as a result of a change in an energy state to a lower one. When a photon is absorbed it is usually not emitted at the same wavelength. The difference is expressed as heat.
Four types:
Crystal Field Effects
Charge Transfer Absorptions
Conduction Bands
Color Centers

7. Electronic Processes Crystal Field Effects
The electronic energy levels of an isolated ion are usually split and displaced when located in a solid. Unfilled d orbitals are split by interaction with surrounding ions and assume new energy values. These new energy values (transitions between them and consequently their spectra) are primarily determined by the valence state of the ion (Fe 2+, Fe3+), coordination number, and site symmetry.

8. Electronic transitions, crystal field effects
Electronic transitions, crystal field effects

9. Electronic Processes Charge-Transfer Absorptions
Absorption bands can also be caused by charge transfers, or inter-element transitions where the absorption of a photon causes an electron to move between ions. The transition can also occur between the same metal in different valence states, such as between Fe2+ and Fe3+. Absorptions are typically strong. A common example is Fe-O band in the uv, causing iron oxides to be red.

10. Electronic transitions (Fe+2, Fe+3), charge transfer (Fe-O)Mg
Diopside Fe
(Mg,Fe)2SiO4
MgCaSi2O6
Electronic transitions
(Fe+2, Fe+3), charge transfer (Fe-O)
(Mg,Fe)SiO3

11. Electronic Processes Conduction Bands
In metals and some minerals, there are two energy levels in which electrons may reside: a higher level called the "conduction band," where electrons move freely throughout the lattice, and a lower energy region called the "valence band," where electrons are attached to individual atoms. The yellow color of gold and sulfur is caused by conduction-band absorption.
Sulfur
Gold
web.syr.edu/~iotz/Gallery.htm

12. Conduction band processes
HgS

13. Vibrational Processes
The bonds in a molecule or crystal lattice are like springs with attached weights: the whole system can vibrate. The frequency of vibration depends on the strength of each spring (the bond in a molecule) and their masses (the mass of each element in a molecule). For a molecule with N atoms, there are 3N-6 normal modes of vibrations called fundamentals.* Each vibration can also occur at multiples of the original fundamental frequency (overtones) or involve different modes of vibrations (combinations).
* In general, a molecule with N atoms has 3N-6 normal modes
of vibration but linear molecules have only 3N-5 normal
modes of vibration as rotation about its molecular axis
cannot be observed.

14. vibrational interactions gases
Vibration-higher energy than rotation
Vibration - harmonic oscillators
stretching, bending
Molecular vibrations cause the multiple absorption bands
HCl
3.75 µm
3.26 µm
35Cl
37Cl

15. Vibrational - rotational modes combine to produce complex
spectra with sharp bands
Vibrational modes
produce simple spectra
Vibration in water molecules

16. X-OH vibrations in minerals: band position in mica shifts with composition
KAl2(AlSi3O10)(F,OH)2

17. Band position in carbonate minerals shifts with composition
MgCO3
CaCO3

18. Si-O bond vibrational resonance
QUARTZ O O
SiO2
Thermal infrared

19. Examples of mineral spectra
Fe2O3
α-FeO(OH)
KFe3(SO4)2(OH)6

20. Spectra of common Earth-surface materials

21. - continuum vs. resonance bands - spectral “mining”
Next lecture
1) reflection/refraction of light from surfaces
(surface interactions)
2) volume interactions
- resonance
- electronic interactions
- vibrational interactions
3) spectroscopy
- continuum vs. resonance bands
- spectral “mining”
- continuum analysis
4) spectra of common Earth-surface materials